Stigma impedes efforts to combat the HIV epidemic by negatively impacting preventive behaviors such as condom use, HIV testing, and engagement in HIV care. Young Black men who have sex with men (YBMSM), the only risk group in the United States experiencing an increase in HIV/AIDS, face multiple forms of stigma related to sexuality, race, and HIV infection. No interventions have been designed to address the effects of these multiple stigmas among HIV-infected and uninfected YBMSM. Novel, sustainable interventions that reduce the impact of stigma and thus improve psychosocial outcomes, reduce risk behaviors, and increase HIV testing and engagement in care among YBMSM are needed to improve individual health, reduce HIV transmission, and decrease healthcare costs. Our research objective is to analyze experiences of multiple stigmas as described and discussed by YBMSM on an online intervention platform and to assess the pathways through which this mode of online social support could mitigate the impact of multiple stigmas on HIV-related outcomes. YBMSM's high access to and use of social networking sites on the internet and on mobile phones emphasizes the relevance of using these technologies for interventions. The study's specific aims are: 1) to analyze stigma-related content contributed by 237 YBMSM enrolled in an ongoing online randomized controlled trial to characterize contributions of multiple stigmas to HIV risk mediators, behaviors, and engagement in care; and 2) to apply structural equation modeling to examine how participants' engagement with stigma content is associated with changes over time in HIV prevention and care behavioral outcomes (e.g., condom use, testing, medication adherence) directly and through proposed mediators (e.g., social support, depression, substance use). The research is innovative in utilizing a unique opportunity to examine how stigma experiences are shared among YBMSM in an online intervention and assessing whether this mode of social support can ameliorate the negative impacts of multiple stigmas on HIV risk behaviors. The eHealth approach capitalizes on broad mobile phone and Internet use among YBMSM of all socioeconomic strata. This research contributes significantly by addressing a critical need to understand and reduce the effects of multiple stigmas in a priority population using an intervention delivered through a cost-effective, highly appealing, popular technology. Our findings will expand understanding of how multiple stigma experiences impact access to and uptake of HIV prevention and care and how a new eHealth-based mode of social support may reduce these negative outcomes among YBMSM. If effective, this form of social support to address stigma via online interventions can readily be scaled up for broad dissemination to reduce HIV transmission and improve care.